What is the appropriate dose of Amoxicillin (Amox) for a 47-pound pediatric patient?

Amoxicillin Dosing for a 47-Pound Pediatric Patient

For a 47-pound (21.3 kg) child using amoxicillin 400mg/5mL suspension, administer 10.6 mL (approximately 11 mL) twice daily for standard respiratory or skin infections, or 21.3 mL twice daily for severe infections or pneumonia. 1

Weight-Based Calculation

• Patient weight: 47 pounds = 21.3 kg 1
• Standard dose (mild to moderate infections): 45 mg/kg/day divided every 12 hours = 479 mg per dose, which equals 10.6 mL of 400mg/5mL suspension twice daily 1, 2
• High dose (severe infections or pneumonia): 90 mg/kg/day divided every 12 hours = 958 mg per dose, which equals 21.3 mL of 400mg/5mL suspension twice daily 1, 2

Indication-Specific Dosing Algorithm

For Mild to Moderate Infections (Ear, Nose, Throat, Skin, Genitourinary)

• Dose: 45 mg/kg/day = approximately 11 mL twice daily 1, 2
• This provides adequate coverage for susceptible Streptococcus pneumoniae, Haemophilus influenzae (non-β-lactamase producing), and Streptococcus pyogenes 1

For Severe Infections or Community-Acquired Pneumonia

• Dose: 90 mg/kg/day = approximately 21 mL twice daily 1, 2
• The Infectious Diseases Society of America recommends this higher dose for severe respiratory infections, areas with >10% penicillin-resistant S. pneumoniae, children <2 years old, recent antibiotic exposure within 30 days, or daycare attendance 1

For Group A Streptococcal Pharyngitis

• Dose: 50-75 mg/kg/day divided into 2 doses for 10 days = approximately 13-16 mL twice daily 1
• Maximum single dose should not exceed 1000 mg 1

Treatment Duration

• Minimum duration: Continue for 48-72 hours beyond symptom resolution 2
• Streptococcal infections: Minimum 10 days to prevent acute rheumatic fever 2
• Pneumonia: 10 days of treatment 1
• Standard respiratory infections: 7-10 days 1

Clinical Monitoring

• Expected improvement: Clinical response should be evident within 48-72 hours of starting therapy 1
• If no improvement: Reevaluate the diagnosis, consider atypical pathogens, assess for complications, or switch antibiotics 1
• Fever resolution: Typically occurs within 24-48 hours for pneumococcal infections, though cough may persist longer 1

Critical Considerations and Common Pitfalls

• Verify suspension concentration: Always confirm you are using 400mg/5mL (not 250mg/5mL or other concentrations) before calculating volume 1
• Maximum daily dose: Do not exceed 4000 mg/day regardless of weight 1
• Shake well before use: Oral suspension must be shaken vigorously before each dose 2
• Storage: Refrigeration is preferable but not required; discard unused suspension after 14 days 2
• Administration: Give at the start of a meal to minimize gastrointestinal intolerance 2

When to Use Amoxicillin-Clavulanate Instead

• Switch to amoxicillin-clavulanate (Augmentin) if the patient has received antibiotics within the past 30 days, has incomplete Haemophilus influenzae type b vaccination, or if β-lactamase-producing organisms are suspected 1, 3
• For treatment failure after 48-72 hours on amoxicillin alone, switch to amoxicillin-clavulanate at 90 mg/kg/day of the amoxicillin component 1, 3